Translocation of proteins across the endoplasmic reticulum (ER) membrane or integration of membrane proteins into the ER membrane comprise the initial steps in the targeting of proteins to the intracellular organelles, to the plasma membrane, or to be secreted outside of the cell. The signal recognition particle (SRP) and the SRP receptor are the components required to selectively recruit proteins targeted to the ER. This molecular machinery is conserved in all cell types examined. SRP RNA is the central component of the SRP, forming a scaffolding for the assembly of SRP proteins and interacting with the ribosome and the SRP receptor. In collaboration with the laboratory of P. Walter, we seek to elucidate the three-dimensional structure of an E. coli SRP RNA homologue by NMR. Three RNAs have been constructed and characterized: a 43 NT sequence for analysis by heteronuclear NMR, and 28 NT and 24 NT sequences for homonuclear analysis. Our aim is to understand the mechanism of this highly conserved cellular process at the molecular level using the facilities of the Computer Graphics Laboratory.